6533b7d4fe1ef96bd1262772

RESEARCH PRODUCT

Energy dependence of the electron-boson coupling strength in the electron-doped cuprate superconductor Pr1.85Ce0.15CuO4−δ

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In the conventional theory of superconductivity the critical temperature Tc is determined by the electron-phonon coupling constant and the phonon cut-off frequency. The hallmark experiments of McMillan and Rowell demonstrated that bosons (phonons) responsible for pairing can be observed through the frequency dependence of the gap parameter. Determination of the electron-boson coupling strength in high-${T}_{c}$ cuprates is, however, not an easy task. One of the promising ways is to measure the energy relaxation rate of photoexcited carriers by using femtosecond real-time techniques. Here, considering the electron relaxation process within the conduction band, it is commonly assumed that the underlying Eliashberg electron-boson coupling function is independent of electron excess energy. Conversely, studies of light-induced suppression of superconductivity in Pr${}_{1.85}$Ce${}_{0.15}$CuO${}_{4}$ reported here imply a strong variation of the electron-boson coupling function on electron energy. Considering the competing scenarios of superconductivity being mediated by either phonons or magnetic excitations, the results suggest that high-energy electrons strongly couple either to phonons or magnetic modes, while the situation is reversed when considering pairing of low-energy electrons.